/*****************************************************************************
*                                                                            *
*  --------------------------------- des.c --------------------------------  *
*                                                                            *
*****************************************************************************/

#include <math.h>
#include <stdlib.h>
#include <string.h>
#include <stdio.h>

/*****************************************************************************
*                                                                            *
*  -------------------------------- bit_get -------------------------------  *
*                                                                            *
*****************************************************************************/

int bit_get(const unsigned char *bits, int pos) {

unsigned char      mask;

int                i;

/*****************************************************************************
*                                                                            *
*  Set a mask for the bit to get.                                            *
*                                                                            *
*****************************************************************************/

mask = 0x80;

for (i = 0; i < (pos % 8); i++)
   mask = mask >> 1;

/*****************************************************************************
*                                                                            *
*  Get the bit.                                                              *
*                                                                            *
*****************************************************************************/

return (((mask & bits[(int)(pos / 8)]) == mask) ? 1 : 0);

}

/*****************************************************************************
*                                                                            *
*  -------------------------------- bit_set -------------------------------  *
*                                                                            *
*****************************************************************************/

void bit_set(unsigned char *bits, int pos, int state) {

unsigned char      mask;

int                i;

/*****************************************************************************
*                                                                            *
*  Set a mask for the bit to set.                                            *
*                                                                            *
*****************************************************************************/

mask = 0x80;

for (i = 0; i < (pos % 8); i++)
   mask = mask >> 1;

/*****************************************************************************
*                                                                            *
*  Set the bit.                                                              *
*                                                                            *
*****************************************************************************/

if (state)
   bits[pos / 8] = bits[pos / 8] | mask;
else
   bits[pos / 8] = bits[pos / 8] & (~mask);

return;

}

/*****************************************************************************
*                                                                            *
*  -------------------------------- bit_xor -------------------------------  *
*                                                                            *
*****************************************************************************/

void bit_xor(const unsigned char *bits1, const unsigned char *bits2, unsigned
   char *bitsx, int size) {

int                i;

/*****************************************************************************
*                                                                            *
*  Compute the bitwise XOR (exclusive OR) of the two buffers.                *
*                                                                            *
*****************************************************************************/

for (i = 0; i < size; i++) {

   if (bit_get(bits1, i) != bit_get(bits2, i))
      bit_set(bitsx, i, 1);
   else
      bit_set(bitsx, i, 0);

}

return;

}

/*****************************************************************************
*                                                                            *
*  ----------------------------- bit_rot_left -----------------------------  *
*                                                                            *
*****************************************************************************/

void bit_rot_left(unsigned char *bits, int size, int count) {

int                fbit,
                   lbit,
                   i,
                   j;

/*****************************************************************************
*                                                                            *
*  Rotate the buffer to the left the specified number of bits.               *
*                                                                            *
*****************************************************************************/

if (size > 0) {

   for (j = 0; j < count; j++) {

      for (i = 0; i <= ((size - 1) / 8); i++) {

         /********************************************************************
         *                                                                   *
         *  Get the bit about to be shifted off the current byte.            *
         *                                                                   *
         ********************************************************************/

         lbit = bit_get(&bits[i], 0);

         if (i == 0) {

            /*****************************************************************
            *                                                                *
            *  Save the bit shifted off the first byte for later.            *
            *                                                                *
            *****************************************************************/

            fbit = lbit;

            }

         else {

            /*****************************************************************
            *                                                                *
            *  Set the rightmost bit of the previous byte to the leftmost    *
            *  bit about to be shifted off the current byte.                 *
            *                                                                *
            *****************************************************************/

            bit_set(&bits[i - 1], 7, lbit);

         }

         /********************************************************************
         *                                                                   *
         *  Shift the current byte to the left.                              *
         *                                                                   *
         ********************************************************************/

         bits[i] = bits[i] << 1;

      }

      /***********************************************************************
      *                                                                      *
      *  Set the rightmost bit of the buffer to the bit shifted off the      *
      *  first byte.                                                         *
      *                                                                      *
      ***********************************************************************/

      bit_set(bits, size - 1, fbit);

   }

}

return;

}

/*****************************************************************************
*                                                                            *
*  Define a mapping for the key transformation.                              *
*                                                                            *
*****************************************************************************/

static const int DesTransform[56] = {

   57, 49, 41, 33, 25, 17,  9,  1, 58, 50, 42, 34, 26, 18,
   10,  2, 59, 51, 43, 35, 27, 19, 11,  3, 60, 52, 44, 36,
   63, 55, 47, 39, 31, 23, 15,  7, 62, 54, 46, 38, 30, 22,
   14,  6, 61, 53, 45, 37, 29, 21, 13,  5, 28, 20, 12,  4

};

/*****************************************************************************
*                                                                            *
*  Define the number of rotations for computing subkeys.                     *
*                                                                            *
*****************************************************************************/

static const int DesRotations[16] = {

   1, 1, 2, 2, 2, 2, 2, 2, 1, 2, 2, 2, 2, 2, 2, 1

};

/*****************************************************************************
*                                                                            *
*  Define a mapping for the permuted choice for subkeys.                     *
*                                                                            *
*****************************************************************************/

static const int DesPermuted[48] = {

   14, 17, 11, 24,  1,  5,  3, 28, 15,  6, 21, 10,
   23, 19, 12,  4, 26,  8, 16,  7, 27, 20, 13,  2,
   41, 52, 31, 37, 47, 55, 30, 40, 51, 45, 33, 48,
   44, 49, 39, 56, 34, 53, 46, 42, 50, 36, 29, 32

};

/*****************************************************************************
*                                                                            *
*  Define a mapping for the initial permutation of data blocks.              *
*                                                                            *
*****************************************************************************/

static const int DesInitial[64] = {

   58, 50, 42, 34, 26, 18, 10,  2, 60, 52, 44, 36, 28, 20, 12,  4,
   62, 54, 46, 38, 30, 22, 14,  6, 64, 56, 48, 40, 32, 24, 16,  8,
   57, 49, 41, 33, 25, 17,  9,  1, 59, 51, 43, 35, 27, 19, 11,  3,
   61, 53, 45, 37, 29, 21, 13,  5, 63, 55, 47, 39, 31, 23, 15,  7

};

/*****************************************************************************
*                                                                            *
*  Define a mapping for the expansion permutation of data blocks.            *
*                                                                            *
*****************************************************************************/

static const int DesExpansion[48] = {

   32,  1,  2,  3,  4,  5,  4,  5,  6,  7,  8,  9,
    8,  9, 10, 11, 12, 13, 12, 13, 14, 15, 16, 17,
   16, 17, 18, 19, 20, 21, 20, 21, 22, 23, 24, 25,
   24, 25, 26, 27, 28, 29, 28, 29, 30, 31, 32,  1

};

/*****************************************************************************
*                                                                            *
*  Define tables for the S-box substitutions performed for data blocks.      *
*                                                                            *
*****************************************************************************/

static const int DesSbox[8][4][16] = {

   {
   {14,  4, 13,  1,  2, 15, 11,  8,  3, 10,  6, 12,  5,  9,  0,  7},
   { 0, 15,  7,  4, 14,  2, 13,  1, 10,  6, 12, 11,  9,  5,  3,  8},
   { 4,  1, 14,  8, 13,  6,  2, 11, 15, 12,  9,  7,  3, 10,  5,  0},
   {15, 12,  8,  2,  4,  9,  1,  7,  5, 11,  3, 14, 10,  0,  6, 13},
   },

   {
   {15,  1,  8, 14,  6, 11,  3,  4,  9,  7,  2, 13, 12,  0,  5, 10},
   { 3, 13,  4,  7, 15,  2,  8, 14, 12,  0,  1, 10,  6,  9, 11,  5},
   { 0, 14,  7, 11, 10,  4, 13,  1,  5,  8, 12,  6,  9,  3,  2, 15},
   {13,  8, 10,  1,  3, 15,  4,  2, 11,  6,  7, 12,  0,  5, 14,  9},
   },

   {
   {10,  0,  9, 14,  6,  3, 15,  5,  1, 13, 12,  7, 11,  4,  2,  8},
   {13,  7,  0,  9,  3,  4,  6, 10,  2,  8,  5, 14, 12, 11, 15,  1},
   {13,  6,  4,  9,  8, 15,  3,  0, 11,  1,  2, 12,  5, 10, 14,  7},
   { 1, 10, 13,  0,  6,  9,  8,  7,  4, 15, 14,  3, 11,  5,  2, 12},
   },

   {
   { 7, 13, 14,  3,  0,  6,  9, 10,  1,  2,  8,  5, 11, 12,  4, 15},
   {13,  8, 11,  5,  6, 15,  0,  3,  4,  7,  2, 12,  1, 10, 14,  9},
   {10,  6,  9,  0, 12, 11,  7, 13, 15,  1,  3, 14,  5,  2,  8,  4},
   { 3, 15,  0,  6, 10,  1, 13,  8,  9,  4,  5, 11, 12,  7,  2, 14},
   },

   {
   { 2, 12,  4,  1,  7, 10, 11,  6,  8,  5,  3, 15, 13,  0, 14,  9},
   {14, 11,  2, 12,  4,  7, 13,  1,  5,  0, 15, 10,  3,  9,  8,  6},
   { 4,  2,  1, 11, 10, 13,  7,  8, 15,  9, 12,  5,  6,  3,  0, 14},
   {11,  8, 12,  7,  1, 14,  2, 13,  6, 15,  0,  9, 10,  4,  5,  3},
   },

   {
   {12,  1, 10, 15,  9,  2,  6,  8,  0, 13,  3,  4, 14,  7,  5, 11},
   {10, 15,  4,  2,  7, 12,  9,  5,  6,  1, 13, 14,  0, 11,  3,  8},
   { 9, 14, 15,  5,  2,  8, 12,  3,  7,  0,  4, 10,  1, 13, 11,  6},
   { 4,  3,  2, 12,  9,  5, 15, 10, 11, 14,  1,  7,  6,  0,  8, 13},
   },

   {
   { 4, 11,  2, 14, 15,  0,  8, 13,  3, 12,  9,  7,  5, 10,  6,  1},
   {13,  0, 11,  7,  4,  9,  1, 10, 14,  3,  5, 12,  2, 15,  8,  6},
   { 1,  4, 11, 13, 12,  3,  7, 14, 10, 15,  6,  8,  0,  5,  9,  2},
   { 6, 11, 13,  8,  1,  4, 10,  7,  9,  5,  0, 15, 14,  2,  3, 12},
   },

   {
   {13,  2,  8,  4,  6, 15, 11,  1, 10,  9,  3, 14,  5,  0, 12,  7},
   { 1, 15, 13,  8, 10,  3,  7,  4, 12,  5,  6, 11,  0, 14,  9,  2},
   { 7, 11,  4,  1,  9, 12, 14,  2,  0,  6, 10, 13, 15,  3,  5,  8},
   { 2,  1, 14,  7,  4, 10,  8, 13, 15, 12,  9,  0,  3,  5,  6, 11},
   },

};

/*****************************************************************************
*                                                                            *
*  Define a mapping for the P-box permutation of data blocks.                *
*                                                                            *
*****************************************************************************/

static const int DesPbox[32] = {

   16,  7, 20, 21, 29, 12, 28, 17,  1, 15, 23, 26,  5, 18, 31, 10,
    2,  8, 24, 14, 32, 27,  3,  9, 19, 13, 30,  6, 22, 11,  4, 25

};

/*****************************************************************************
*                                                                            *
*  Define a mapping for the final permutation of data blocks.                *
*                                                                            *
*****************************************************************************/

static const int DesFinal[64] = {

   40,  8, 48, 16, 56, 24, 64, 32, 39,  7, 47, 15, 55, 23, 63, 31,
   38,  6, 46, 14, 54, 22, 62, 30, 37,  5, 45, 13, 53, 21, 61, 29,
   36,  4, 44, 12, 52, 20, 60, 28, 35,  3, 43, 11, 51, 19, 59, 27,
   34,  2, 42, 10, 50, 18, 58, 26, 33,  1, 41,  9, 49, 17, 57, 25

};

/*****************************************************************************
*                                                                            *
*  Define a type for whether to encipher or decipher data.                   *
*                                                                            *
*****************************************************************************/

typedef enum DesEorD_ {encipher, decipher} DesEorD;

/*****************************************************************************
*                                                                            *
*  -------------------------------- permute -------------------------------  *
*                                                                            *
*****************************************************************************/

static void permute(unsigned char *bits, const int *mapping, int n) {

unsigned char      temp[8];

int                i;

/*****************************************************************************
*                                                                            *
*  Permute the buffer using an n-entry mapping.                              *
*                                                                            *
*****************************************************************************/

memset(temp, 0, (int)ceil(n / 8));

for (i = 0; i < n; i++)
   bit_set(temp, i, bit_get(bits, mapping[i] - 1));

memcpy(bits, temp, (int)ceil(n / 8));

return;

}

/*****************************************************************************
*                                                                            *
*  ------------------------------- des_main -------------------------------  *
*                                                                            *
*****************************************************************************/

static int DES_main(const unsigned char *source, unsigned char *target, const
   unsigned char *key, DesEorD direction) {

static unsigned char subkeys[16][7];

unsigned char        temp[8],
                     lkey[4],
                     rkey[4],
                     lblk[6],
                     rblk[6],
                     fblk[6],
                     xblk[6],
                     sblk;

int                  row,
                     col,
                     i,
                     j,
                     k,
                     p;

/*****************************************************************************
*                                                                            *
*  If key is NULL, use the subkeys as computed in a previous call.           *
*                                                                            *
*****************************************************************************/

if (key != NULL) {

   /**************************************************************************
   *                                                                         *
   *  Make a local copy of the key.                                          *
   *                                                                         *
   **************************************************************************/

   memcpy(temp, key, 8);

   /**************************************************************************
   *                                                                         *
   *  Permute and compress the key into 56 bits.                             *
   *                                                                         *
   **************************************************************************/

   permute(temp, DesTransform, 56);

   /**************************************************************************
   *                                                                         *
   *  Split the key into two 28-bit blocks.                                  *
   *                                                                         *
   **************************************************************************/

   memset(lkey, 0, 4);
   memset(rkey, 0, 4);

   for (j = 0; j < 28; j++)
      bit_set(lkey, j, bit_get(temp, j));

   for (j = 0; j < 28; j++)
      bit_set(rkey, j, bit_get(temp, j + 28));

   /**************************************************************************
   *                                                                         *
   *  Compute the subkeys for each round.                                    *
   *                                                                         *
   **************************************************************************/

   for (i = 0; i < 16; i++) {

      /***********************************************************************
      *                                                                      *
      *  Rotate each block according to its round.                           *
      *                                                                      *
      ***********************************************************************/

      bit_rot_left(lkey, 28, DesRotations[i]);
      bit_rot_left(rkey, 28, DesRotations[i]);

      /***********************************************************************
      *                                                                      *
      *  Concatenate the blocks into a single subkey.                        *
      *                                                                      *
      ***********************************************************************/

      for (j = 0; j < 28; j++)
         bit_set(subkeys[i], j, bit_get(lkey, j));

      for (j = 0; j < 28; j++)
         bit_set(subkeys[i], j + 28, bit_get(rkey, j));

      /***********************************************************************
      *                                                                      *
      *  Do the permuted choice permutation.                                 *
      *                                                                      *
      ***********************************************************************/

      permute(subkeys[i], DesPermuted, 48);

   }

}

/*****************************************************************************
*                                                                            *
*  Make a local copy of the source text.                                     *
*                                                                            *
*****************************************************************************/

memcpy(temp, source, 8);

/*****************************************************************************
*                                                                            *
*  Do the initial permutation.                                               *
*                                                                            *
*****************************************************************************/

permute(temp, DesInitial, 64);

/*****************************************************************************
*                                                                            *
*  Split the source text into a left and right block of 32 bits.             *
*                                                                            *
*****************************************************************************/

memcpy(lblk, &temp[0], 4);
memcpy(rblk, &temp[4], 4);

/*****************************************************************************
*                                                                            *
*  Encipher or decipher the source text.                                     *
*                                                                            *
*****************************************************************************/

for (i = 0; i < 16; i++) {

   /**************************************************************************
   *                                                                         *
   *  Begin the computation of f.                                            *
   *                                                                         *
   **************************************************************************/

   memcpy(fblk, rblk, 4);

   /**************************************************************************
   *                                                                         *
   *  Permute and expand the copy of the right block into 48 bits.           *
   *                                                                         *
   **************************************************************************/

   permute(fblk, DesExpansion, 48);

   /**************************************************************************
   *                                                                         *
   *  Apply the appropriate subkey for the round.                            *
   *                                                                         *
   **************************************************************************/

   if (direction == encipher) {

      /***********************************************************************
      *                                                                      *
      *  For enciphering, subkeys are applied in increasing order.           *
      *                                                                      *
      ***********************************************************************/

      bit_xor(fblk, subkeys[i], xblk, 48);
      memcpy(fblk, xblk, 6);

      }

   else {

      /***********************************************************************
      *                                                                      *
      *  For deciphering, subkeys are applied in decreasing order.           *
      *                                                                      *
      ***********************************************************************/

      bit_xor(fblk, subkeys[15 - i], xblk, 48);
      memcpy(fblk, xblk, 6);

   }

   /**************************************************************************
   *                                                                         *
   *  Do the S-box substitutions.                                            *
   *                                                                         *
   **************************************************************************/

   p = 0;

   for (j = 0; j < 8; j++) {

      /***********************************************************************
      *                                                                      *
      *  Compute a row and column into the S-box tables.                     *
      *                                                                      *
      ***********************************************************************/

      row = (bit_get(fblk, (j * 6)+0) * 2) + (bit_get(fblk, (j * 6)+5) * 1);
      col = (bit_get(fblk, (j * 6)+1) * 8) + (bit_get(fblk, (j * 6)+2) * 4) +
            (bit_get(fblk, (j * 6)+3) * 2) + (bit_get(fblk, (j * 6)+4) * 1);

      /***********************************************************************
      *                                                                      *
      *  Do the S-box substitution for the current six-bit block.            *
      *                                                                      *
      ***********************************************************************/

      sblk = (unsigned char)DesSbox[j][row][col];

      for (k = 4; k < 8; k++) {

         bit_set(fblk, p, bit_get(&sblk, k));
         p++;

      }

   }

   /**************************************************************************
   *                                                                         *
   *  Do the P-box permutation to complete f.                                *
   *                                                                         *
   **************************************************************************/

   permute(fblk, DesPbox, 32);

   /**************************************************************************
   *                                                                         *
   *  Compute the XOR of the left block and f.                               *
   *                                                                         *
   **************************************************************************/

   bit_xor(lblk, fblk, xblk, 32);

   /**************************************************************************
   *                                                                         *
   *  Set the left block for the round.                                      *
   *                                                                         *
   **************************************************************************/

   memcpy(lblk, rblk, 4);

   /**************************************************************************
   *                                                                         *
   *  Set the right block for the round.                                     *
   *                                                                         *
   **************************************************************************/

   memcpy(rblk, xblk, 4);

}

/*****************************************************************************
*                                                                            *
*  Set the target text to the rejoined final right and left blocks.          *
*                                                                            *
*****************************************************************************/

memcpy(&target[0], rblk, 4);
memcpy(&target[4], lblk, 4);

/*****************************************************************************
*                                                                            *
*  Do the final permutation.                                                 *
*                                                                            *
*****************************************************************************/

permute(target, DesFinal, 64);

return 0;

}

/*****************************************************************************
*                                                                            *
*  ----------------------------- DES_encipher -----------------------------  *
*                                                                            *
*****************************************************************************/

void DES_encipher(const unsigned char *plaintext, unsigned char *ciphertext,
   const unsigned char *key) {

DES_main(plaintext, ciphertext, key, encipher);

return;

}

/*****************************************************************************
*                                                                            *
*  ----------------------------- DES_decipher -----------------------------  *
*                                                                            *
*****************************************************************************/

void DES_decipher(const unsigned char *ciphertext, unsigned char *plaintext,
   const unsigned char *key) {

DES_main(ciphertext, plaintext, key, decipher);

return;

}

